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形容詞・形容動詞. Japanese doesn't technically have adjectives, but special types of nouns and verbs called na-adjectives and i-adjectives respectively have the same function.
副詞. Words that typically modify 用言 (words that inflect and function as predicators, such as verbs and adjectives). However, 副詞 also modify other constituents, including other adverbs, nouns (under li…
アイヌ語. A moribund language spoken by some Ainu, an indigenous people mainly living on the island of Hokkaidō. It is not regarded as related to Japanese.
曖昧な表現. A situation where multiple interpretations are possible as a result of scarcity of information. Ambiguity can exist at the grammatical and lexical level, and is usually resolved through context…
古語. Old words or phrases no longer in general spoken or written use.
相（アスペクト）. A verbal category mainly indicating the speaker's view of the temporal structure of the situation the clause describes, such as whether it is habitual or complete.
当て字. Kanji assigned to words based on their sound rather than their meaning.
助動詞. Inflecting function words or endings such as 〜ます and 〜ない. Many inflect like verbs (such as 〜(ら)れる), but many others do not (such as 〜たい), so here we will call these simply "auxiliaries" and not …
過去の補助動詞. Auxiliary indicating past directly as it was perceived by the speaker whereas けり expresses past hearsay. [せ｜◯｜き｜し｜しか｜◯]
過去の推量・原因推量・伝聞・婉曲の補助動詞. Auxiliary for showing past deduction, past hypothetical cause, past hearsay, past circumlocution. [◯｜◯｜けむ（けん）｜けむ（けん）｜けめ｜◯]
打消しの補助動詞. Classical auxiliary for negating a predicate, having the same function as ない. This auxiliary is still commonly found in fixed patterns (e.g. ~ざるを得ない or ~ずに) or its 連体形 can merely be used ins…
完了・強意・並列の補助動詞. Auxiliary for showing completion, strong will and for enumeration. [ね｜に｜ぬ｜ぬる｜ぬれ｜ね]. This auxiliary should not be mixed up with the 連体形 of ず.
美化語. Making words polite (美化 lit. "beautification") by adding the prefix 御 (お・ご) to a word.
For the grammar and variants of Japanese words and phrases considered to be mainly used in casual speech or conversation.
使役. Japanese has a causative morpheme -(s)ase-, which turns verbs into causative verbs. Japanese also has a number of lexical causative verbs, as well.
For questions about the ways in which children learning Japanese (as a first language) speak differently from adults.
中国語. Although totally unrelated, the Chinese language has had perhaps a greater impact on the Japanese language than Latin has had on English, especially in the form of a vast number of loanwords and …
文語（古文）. The classical literary form of the language based on Early Middle Japanese.
分裂文. Sentences "clefted" into two parts. In Japanese, these commonly take the the form 〜のは〜だ or 〜のが〜だ, putting focus on the precopular constituent.